The present invention relates to a data-processing apparatus having a bitblt (bit boundary block transfer) unit for transferring data between memories at high speed.
Recently, work stations have been developed which can process various types of data, such as characters, graphics and images. The general trend is that the new data-output technique known as "bit map control" is used in the work stations of this kind, in order to provide image data which is easy for users to understand. The bit map control requires a high-speed data transfer unit, generally called a "bitblt unit," in order to quickly display characters in desired positions on the screen of a display. The term "bitblt" stands for "bit boundary block transfer," and is also known as a "raster operation." This technique of transferring data at high speed consists of designating, in the unit of bits, a desired one o the data pieces stored in a display memory, then transferring the data piece to a display, and finally displaying the data piece in a desired rectangular region of the screen of the display.
In such a work station, character data, such as Chinese characters and alphanumeric characters, is transferred between a main memory and a display memory. It will now be briefly explained how the data is transferred.
First, the CPU in the work station sets parameter data in the parameter file provided within a bitblt unit. The parameter data is necessary for transferring characters, one by one, from the main memory to the display memory, or vice versa. It consists of addresses, data lengths, and the like. More precisely, the parameter data includes:
(1) Source address upper bit PA1 (2) Source address lower bit PA1 (3) Destination address upper bit PA1 (4) Destination address lower bit PA1 (5) Source x-direction length PA1 (6) Destination x-direction length PA1 (7) Source y-direction length PA1 (8) Destination y-direction length PA1 (9) Source x-direction scaler PA1 (10) Destination x-direction scaler PA1 (11) Source y-direction scaler PA1 (12) Destination y-direction scaler PA1 (13) Source address-increment upper bit PA1 (14) Source address-increment lower bit PA1 (15) Source address-skip upper bit PA1 (16) Source address-skip lower bit PA1 (17) Destination address-skip upper bit PA1 (18) Destination address-skip lower bit PA1 (19) Source x-direction displacement PA1 (20) Destination x-direction displacement PA1 (21) Source y-direction displacement PA1 (22) Destination y-direction displacement PA1 (23) Source x-direction scaler displacement PA1 (24) Destination x-direction scaler displacement PA1 (25) Source y-direction scaler displacement PA1 (26) Destination y-direction scaler displacement
Then, the data transfer circuit provided in the work station reads the data from the parameter file. In accordance with the data, the circuit generates interrupts, each after any one-character of data has been transferred. These interrupts are supplied to the CPU.
Most of the parameters required for transferring Chinese characters and alphanumeric characters are fixed or invariable. In the conventional method of transferring data, one parameter must be provided for one character. Hence, the data cannot be processed at high speed. Further, since one interrupt must be generated upon completion of transfer of each character, the CPU will inevitably be overloaded.